Georgy Arbatov, 87, a foreign policy adviser to Soviet presidents who served as the country's top America-watcher during the Cold War, died Oct. 1, it was reported from Moscow. No details of the death were disclosed.

Mr. Arbatov, who advised leaders from Leonid Brezhnev to Mikhail Gorbachev and was especially close to Yuri Andropov, was credited in the West and later in Russia for understanding that the Soviet system was fundamentally untenable.

"He belonged to a group of reformers who believed that the Soviet system could be and had to be reformed," Yevgeny Primakov, who served as Russian prime minister under Boris N. Yeltsin, told state news channel Rossiya-24.

"His name is associated with the entire epoch of the Soviet Union. . . . He was part of the closest and best-trusted consultants of Brezhnev and Andropov," Primakov said.

From 1967 to 1995, Mr. Arbatov ran the U.S. and Canada Institute, an advisory body to Soviet authorities that he founded and that had huge sway over policy toward the American continent at a time of heightened tensions for the Cold War adversaries.

Mr. Arbatov, who studied international law but started out as a journalist after fighting in World War II, penned speeches for leaders including Brezhnev.

Mr. Arbatov was awarded the highest Soviet scientific distinction in 1974, Academician of the Academy of Sciences of the U.S.S.R.